Filip
XS650 Member
I got some new .5mm oversize pistons and rings (second oversize) for my xs650. What should I have my machinist bore my cylinders to? This is the first time I am having this work done and I am unsure of the correct tolerances.
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Cylinder bore for .5mm oversize pistons and rings
Clearance spec for between the pistons and cylinders is .050-.055mm, or about .0019"-.0022". So, take your new pistons in with the cylinder so the machinist can measure them, provide him with that clearance spec, and he'll bore them accordingly.
Filip
XS650 Member
Thanks!
Mickster
XS650 Enthusiast
I did the exact same thing to mine. Gave a speed shop the cylinders and pistons with the specs photo copied from the shop manual. They advised me that they don't have to bore the cylinders, they just honed them to the exact specs.
Just curious, at .5mm over, will they actually bore or will they hone the cylinders to size? Regardless of the process I agree all the pieces should go with the cylinder to the machinist for proper sizing.
A lot of shops have a hard time with .5mm bore so they try to hone to size. If the cylinders are straight without any taper it can be done. I have never had a cylinder on these older bikes that haven't had some taper. Sure you could hone them and it will probably work ok. Most shops I deal with like at least 1mm over pistons so they can properly bore and hone to the supplied piston.
That’s what I suspected. Had my car engine done last year and was able to hone to size as surprisingly there was negligible taper in the bores. I’m sure that honing will be fine for a street use motor.
Just depends on the bore condition.
